Mössbauer measurements in CuFeTe 2 (original) (raw)
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SDW in the 2D Compound CuFeTe 2
Hyperfine Interactions, 2001
In a previous work (ICAME'97) we presented the Mssbauer results for a non-stoichiometric sample of the quasi-two-dimensional (2D) dichalcogenide CuFeTe2, where a Spin Density Wave (SDW) ground state with T SDW=25615 K was proposed. Here we report the study of the magnetic and electric properties determined by magnetic susceptibility, Mssbauer spectroscopy and resistance measurements, of an almost stoichiometric sample prepared by the vertical Bridgman growth technique. The SDW behavior is supported by the results obtained by the following different techniques: Magnetic susceptibility: A magnetic transition is observed at T SDW=308 K with a Pauli paramagnetic behavior above this temperature. Mssbauer effect: The shape of the spectra and the thermal evolution of the hyperfine field are characteristic of the SDW's in quasi-2D systems. Electrical resistance: There is a metal–semiconductor transition along the layers as the temperature decreases indicating the opening of a gap ...
2010
In the tetragonal crystalline structure of MnxFe1−xSe0.85, the magnetic state contains low-and high-spin Fe 2+ , with high-spin numbers equal to that of the combined Mn substitute and Se deficiency atoms. The state is pinned by "spin-hopping" around substitution centers via highspin ↔ low-spin conversions. During the structural distortion from tetragonal to orthorhombic, from 90 K to 70 K, the rate of spin conversions increases and the iterant character of the magnetic state is enhanced. In the orthorhombic structure, the spin dynamics evolve into an incommensurate spin-density wave (ISDW). Excitations of the ISDW decrease with temperature and level out across the superconducting phase. The ISDW appears to have more than one oscillation mode and contributions from high-order harmonics.
Evidence of magnetic broadening in Mössbauer spectra of superconducting FeTe 0.8 S 0.2
Hyperfine Interactions, 2013
Magnetic properties of the FeTe 0.8 S 0.2 superconductor were studied by Mössbauer spectroscopy. Low-velocity Mössbauer spectra that were recorded in the temperature range from 5.7 K up to 300 K show a paramagnetic doublet with a broadening at temperatures below 77 K. The broadening can be explained by the appearance of a distribution of hyperfine magnetic fields due to the magnetic ordering of a part of the sample. The magnetically ordered fraction starts to decrease at temperatures below 20 K indicating a possible competition with the onsetting superconductive state.
Physical Review B, 2011
Polarized Raman-scattering spectra of non-superconducting, single-crystalline FeTe are investigated as function of temperature. We have found a relation between the magnitude of ordered magnetic moments and the linewidth of 1g A phonons at low temperatures. This relation is attributed to the intermediate spin state (S=1) and the orbital degeneracy of the Fe ions. Spin-phonon coupling constants have been estimated based on microscopic modeling using density-functional theory and analysis of the local spin density. Our observations show the importance of orbital degrees of freedom for the Fe-based superconductors with large ordered magnetic moments, while small magnetic moment of Fe ions in some iron pnictides reflects the low spin state of Fe ions in those systems.
63,65Cu NMR study of the magnetically ordered state of the multiferroic CuFeO2
Journal of Magnetism and Magnetic Materials, 2020
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Magnetic ordering and ergodicity of the spin system in the Cu2Te2O5X2 family of quantum magnets
Physical Review B, 2006
We present an experimental and theoretical study of the magnetically frustrated spin system in pure and substitutionally disordered compounds from the Cu 2 Te 2 O 5 X 2 family of quantum magnets. Experimental magnetic susceptibilities and specific heats were analyzed simultaneously using models of ͑i͒ isolated tetrahedra of four antiferromagnetically coupled Cu 2+ spins and ͑ii͒ coupled tetrahedra within one-dimensional chains, in both cases involving mean-field coupling to other chains. The results show that Cu 2 Te 2 O 5 X 2 compounds are true three-dimensional systems of coupled spins. Susceptibility results are consistent with the existence of a singlet-triplet gap, whereas specific heat analysis shows that the singlet-triplet gap is filled with dense singletlike excitations that contribute to finite specific heat at temperatures far below the singlet-triplet gap, but do not contribute to a magnetic response of the system. Furthermore, measured specific heat data show excessive entropy when compared to the numerical results based on a pure spin system, which we attribute to the presence of phonons. Though Cu 2+ spins are arranged in a geometrically frustrated tetrahedral antiferromagnetic configuration and spin correlation length extends beyond the single tetrahedral cluster dimension, Cu 2 Te 2 O 5 X 2 compounds do not exhibit ergodicity breaking at low temperatures, in contrast to the related geometrically frustrated kagomé and pyrochlore antiferromagnets.
reprint Superparamagnetism in CuFeInTe 3 and CuFeGaTe 3 alloys
The temperature dependencies of DC magnetic susceptibilities, x(T), of CuFeInTe 3 and CuFeGaTe 3 alloys were measured in a SQUID apparatus using the protocol of field cooling (FC) and zero FC (ZFC). The FC curves of both samples reflect a weak ferromagnetic (or ferrimagnetic) behavior with a nearly constant value of x(T) in the measured temperature range (2–300 K) indicating that the critical temperatures (T c) are >300 K. The ZFC curves diverges from FC, showing irreversibility temperatures (T irr) of $250 K for CuFeInTe 3 and >300 K for CuFeGaTe 3 , suggesting that we are dealing with cluster-glass systems in a superparamagnetic state. ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Since the discovery of room tempera-ture, ferromagnetism in II-IV-V 2 chalcopyrite compounds, alloyed with manganese, the investigation on these alloys has received renewed interest [1–8]. Moreover, theoretical calculations predicted that room-temperature ferromagnet-ism can also...
A new look on the nature of high-spin to low-spin transition in Fe2O3
Iron sesquioxide (Fe2O3) displays pressure and temperature induced spin and structural transitions. Our calculations show that, density functional theory (DFT), in the generalized gradient approximation (GGA) scheme, is capable of capturing both the transitions. The ambient pressure corundum type phase (hematite or α-Fe2O3), having R3 c symmetry, gets distorted by the application of pressure and transforms to a distorted corundum type or Rh2O3(II) phase with P bcn symmetry, in agreement with recent experiments. GGA + U calculations show the same trend but shift the transition pressures to higher values. Experimentally, the onset of the structural transition begins in the vicinity of the spin transition pressure and whether the system undergoes spin transition in the corundum type (HP1) or in the Rh2O3(II) type (HP2) phase, is still a controversial issue. With a relatively simple, but general, octahedral structural parameter, Voct (the octahedral volume around iron ions), we show that in order to acquire a low spin (LS) state from a high spin (HS) one, the system does not necessarily need to change the crystal structure. Rather, the spin transition is a phenomenon that concerns the cation octahedra and the spin state of the system depends mainly on the value of Voct, which is governed by two distinct equations of state, separated by a well defined volume gap, for the HS and LS states respectively. Analysis of the results on the basis of octahedral volume allows to sum up and bridge the gap between two experimental results and thus provides a better description of the system in the region of interest.